From the Latin, "Anno Domini," which means in the year of our Lord. The Western Calendar is dated from the birth of Christ. Therefore, A.D. 2000 means 2000 years after the birth of Jesus. So, A.D. Is used when citing dates. It can be used as AD 2000, 2000 AD, a.d. 2000, 2000 a.d., or 2000 ad.